The invention relates to a filter press with a stack of vertically oriented or aligned, horizontally displaceable filter plates. Adjacent one of the filter plates are mutually coupled via at least one connecting element each. A respective filter chamber is defined between adjacent ones of the filter plates. The filter plates lie against one another with sealing edges in a pressing position of the stack of filter plates, and are displaceable successively to a discharge position by the horizontal displacement of at least one filter plate, in which discharge position the horizontal distance of adjacent filter plates is limited by the action of a coupling element of a filter plate on a stop surface of the connecting element of an adjacent filter plate.
Such a filter plate is known from DE 44 28 963 C1 for example. The connecting elements are arranged as levers which are swivelably held on laterally projecting projections of the filter plates. The levers are provided with two arms each, namely an arm with a holding hook which with respect to the opening direction is at the rear and is latched behind the projection of the next filter plate at the rear in the pressing or filtering position. Moreover, the levers comprise a front arm which is provided with a control surface which during the movement away of the next filter plate at the front, once the same has moved away over a predetermined path, produces a swiveling movement of the lever by cooperating with its projection and during which its holding hook detaches from the projection of the next filter plate at the rear. In this process the control surface encloses a recess in the hook-like front arm of the lever in which the projection of the next filter plate at the front is continually received and is provided at its base with the stop surface for fixing, i.e. limiting the plate distance in the discharge position.
The levers thus fulfill a double function by mutually locking the adjacent filter plates based on the pressing position on the one hand and thus preventing that swelling filter cake will lead to the expulsion of such filter plates which should not yet be emptied, and by acting as connecting elements on the other hand which in the discharge position of the filter plates define their maximum distance with respect to one another.
A typical aspect for the known filter press is the sequential emptying of only one filter chamber successively, with the as yet unemptied filter chambers remaining mutually locked until immediately before the discharging process. The known filter press is not suitable for discharging principles in which a section of the stack consisting of a plurality of filter plates is to be unlocked simultaneously, since the unlatching of the filter plates can always only occur successively.
From DE 43 25 055 A1 a filter press is known whose filter plates are mutually chained together by brackets and connecting links. Whereas the brackets are swivelably held on a filter plate, the connecting brackets connect one each of the brackets with an adjacent filter plate in a flexible way. A hook is each arranged on the brackets which latches into projections on the filter plates when the filter plates are pushed together into a stack. The joints between the brackets and the connecting links are disposed in such a way that when two adjacent filter plates are pulled apart the hook which is latched into the projection of the next following filter plate will detach from this projection to the amount to which the bracket which belongs to said hook with the connecting link pulling the same assumes a stretched position. It is to be prevented in this way that intermediate spaces will open prematurely between the filter plates during the opening of the filter press in which emerging filter cakes could get stuck.
If the plate stacks were opened in sections in this known filter plate it is also not ensured in this case that the discharge distance between adjacent plates in all sections would be of the same size because a relief of the sealing edges decreases continually with rising distance of the filter plate from the movable head plate prior to the pulling apart of the stack of plates after the relief, i.e. removal of the locking pressure.
The invention is based on the object of further developing a filter press in such a way that during a sequential discharge of complete sections of the stack of plates, always the same discharge distance of adjacent filter plates can be achieved during the discharge of all sections. The connecting elements should simultaneously comprise a latching function for the filter plates of the sections not yet designated for discharge and a connecting function for maintaining the discharge distance.
Based on a filter press of the kind described above, this object is achieved in accordance with the invention in such a way that the filter plates, based on the pressing position, can be displaced to a relief position by displacing a filter plate in which the sealing edges of the filter plates are detached from the associated sealing surfaces and in which the coupling elements rest on a blocking surface of the connecting elements which prevents the further horizontal spacing of adjacent filter plates, with the contact of the coupling elements on the blocking surfaces being removable by unlatching the associated connecting elements, so that a further displacement of adjacent filter plates to the discharge position is possible.
After ending the actual filtration process, the opening and discharging process occurs as follows in the press in accordance with the invention:
At first, a relief of all filter plates is achieved by the displacement of the first filter plate (as seen from the pressing plate) and subsequently all further filter plates in such a way that the connecting elements allow an only very small distance of adjacent filter plates, so that a transmission of the tensile force from one filter plate to the next occurs once its distance is merely a few millimeters. This small distance of adjacent filter plates from one another is necessary, however, in order to achieve a relief of the sealing edges of the filter plates which are under a pretension in the pressing position. In the relieved state the sealing edges typically project a few millimeters above the surface of the filter plates in order to achieve the required sealing of the filter chambers in the pressing position of the packet due to the elastic deformation. The transfer of all filter plates from the pressing position to the relief position occurs appropriately for the entire stack of plates in one job step, namely preferably by using the closing cylinder in that the same is moved back by the sum total of the individual relief distances.
The advantage of the solution in accordance with the invention is that with the help of the connecting elements in accordance with the application it is possible to produce an active relief of the sealing edges of the entire stack of plates before the plates of the first section are brought to the discharge distance. This active relief ensures that the filter plates will all have the same distance with respect to each other as defined by the connecting brackets and that in this position the sealing edges of the filter plates are completely relieved. Only in this way is it possible to prevent that during a xe2x80x9cmigrationxe2x80x9d of the discharge section from the first to the last section of the stack of plates an even discharge distance is maintained.
In apparatuses according to the state of the art the discharge distance of the sections emptied at a later time is decreased more and more in such a way that the sealing edges of the associated plates have become relieved less and less by their own power in the case of missing preceding active relief. This relief occurs in apparatuses according to the state of the art at the time at which plates are actually pulled apart to the discharge distance, as a result of which, especially when a plurality of filter plates is concerned, a far from inconsiderable measure of length is obtained by addition which reduces the available discharge distance. One must consider that the sections to be emptied, with the exception of the first section, are disposed right in the middle of the stack of filter plates and thus a displacement of the entire stack of plates by providing the required discharge distance is usually impossible.
The cake discharge and the removal of the filter plates delimiting the filter cake to the discharge distance as required for this purpose only occurs in a second step, namely by unlatching in a preceding step the connecting elements of the filter plates of the section which is to be discharged as the next one.
After their unlatching, the connecting elements act like elements with an increased length, so that in the case of a renewed tensile load on the filter plates with unlatched connecting elements the same are displaced to discharge distance with respect to each other, with the connecting elements defining said discharge distance and thus also ensuring a permanent interlinking of the filter plates in the discharge position.
Preferably, the filter plates of a first discharged section are pressed together again after the unlatching of the connecting elements of the second section which is to be discharged next so as to keep down the longitudinal extension of the filter press. Within such a discharge principle, a section with filter plates in the discharge distance xe2x80x9cpasses throughxe2x80x9d the entire stack of plates from one end to the other, so that its overall length, after the one-time opening of the first section, remains unchanged and the zone of a lower xe2x80x9cdensityxe2x80x9d of the filter plates migrates through the stack.
In comparison with known presses in which the stack of plates is not transferred to a relief position with defined plate distances prior to the opening of the first section, but merely the pressure of the closing cylinder is removed and thus a self-relief occurs which is produced by the spring properties of the sealing edges, the advantage as offered by the invention is that during the discharge of all sections there is now a defined discharge distance. As seen from the closing cylinder, there is in the known filter press a self-relief of the sealing edges which decreases continually with increasing distance, which is caused by the fact that the sealing edges of the filter plates which are farther away from the closing cylinder would have to displace, during their extension, in the horizontal direction all previously situated filter plates. The frictional forces of the plate bearings in the press frame, which add up and counteract such an independent plate displacement, will reach a value from a certain number of plates which exceeds the restoring force of the compressed sealing edges even in the pressed position, so that at first there is no self-resetting of the filter plates which are farther away from the closing cylinder despite the pressure relief of the stack of plates.
When the stack of plates migrates through the discharge section, its width decreases continually with rising distance from the closing cylinder, which means also the discharge distance between the filter plates, because the self-restoration of the sealing edges which still substantially occurred in the first section only occurs incompletely or not at all in the sections that are farther away. When plates of an already emptied section are pushed together, they are not pressed together with such a force that the sealing edges are brought to the compressed state again as would be typical for the pressed position in which the closing force is applied by the closing cylinder. As a result, the discharge distance between the filter plates of the sections farther away continually decreases by a certain amount, which will be particularly disadvantageous in cases when it is necessary to intervene with auxiliary apparatuses in the intermediate space between adjacent filter plates in order to ensure a secure discharge of cake or to perform the cleaning of a filter cloth.
As a result of the active tensile relief of the stack of plates with the help of the closing cylinder for example, the setting of a defined distance of the filter plates with respect to one another occurs in the filter press in accordance with the invention. The introduction of a tensile force into only one filter plate is sufficient due to the connecting elements. Based on such a relief state of the stack of filter plates, the same discharge distance between the filter plates is ensured during the subsequent discharge of all sections.
In a preferred embodiment, the connecting elements are embodied as connecting brackets which are each provided with a groove in which the coupling element, which is embodied as a coupling pin, of an adjacent filter plate.
In a further development of the invention it is provided that the connecting elements are held in a swivelable manner and comprise a groove which is offset in its longitudinal direction and is provided with a first section with the blocking surface and a minimal groove width which corresponds to the width of the coupling element with respect to the relief distance and a second section with the stop surface disposed on the face side.
When the connecting elements are each swivelable about the axis of a coupling pin, the same fulfills a double function, namely acting on the one hand as a coupling element in the groove of the connecting element of the subsequent filter plate and, on the other hand, as a bearing element for the connecting element of the filter plate just considered.
According to a further development of the filter press in accordance with the invention, it is proposed that the connecting elements are provided with a first arm with the groove and a second arm which is opposite of the first arm with respect to the swivel axis and which extends above the swivel axis and can be pressed downwardly by means of the unlatching device, so that the coupling element can enter the second section of the groove.
It is further particularly advantageous when the connecting elements are disposed in two mutually parallel planes, with adjacent connecting elements being disposed in different planes. In this way a scaled arrangement of the connecting elements is avoided as is realized in DE 44 28 963 C1.
It is finally provided that the unlatching device is a carriage that is horizontally displaceable in the press frame and that is provided with a runner which is adjustable in the vertical direction. Appropriately, the carriage is additionally provided with a displacement device for the filter plates in order to omit longitudinally extending actuating elements as would otherwise possibly be required in connection with a stationary displacement device.